The present invention relates to a lifting device for the presser foot of a sewing machine.
Conventional lifting devices such as, for example, the one disclosed in Swiss Pat. No. 532,150, are in most cases relatively cumbersome in operation, i.e., they contain one or even two operating elements which are operated in different ways by hand and are located in the zone of the stitching site or on the rear side of the head of the machine. Apart from the fact that these devices in most cases involve a complicated construction, they can only be operated with great difficulty, especially by the handicapped. Devices of this type, which can be operated by the knee or the foot, have been proposed, for example, in East German Pat. No. 53,542, wherein an operating lever is provided which is operable always toward the same side by the foot or knee for the lifting as well as the lowering of the presser foot. However, the motion transmission to the presser foot and/or the arresting of the latter in its upper end position require relatively complicated lever and spring systems which not only occupy a relatively large amount of space but also demand a relatively large amount of energy, and are susceptible to disturbances.
The present invention avoids these disadvantages. The device of the present invention comprises an operating lever operable in the same direction for lifting and lowering the presser foot. The presser foot, which is under a spring force in its lowering direction, is characterized in that a double lever is operatively connected at one end to the operating lever and engaged at its other end with a presser bar counteracting the spring force, and the double lever is operatively connected to a guide arm between this point of engagement and its pivot bearing. The guide arm contains a detent member guided in an inherently closed and defined path. Starting from a lower detent location, the curved path has a first path section ascending to a first upper stop and thereafter descending to a catch detent, followed by a second path section likewise ascending to a second upper stop and then returning to the lower detent location. When the detent member is positioned in the lower catch detent, the presser foot assumes its lower final position wherein a first operation of the operating lever lifts the detent member along the first path section up to the first upper stop. When the operating lever is released, the detent member automatically falls into the catch detent determining the lifted position of the presser foot. Upon a renewed operation of the operating lever, the detent member is lifted from the detent into the second path section up to the second upper stop thereof. Upon the renewed release of the operating lever, the detent member automatically returns to the lower detent location.
The confined guidance of the detent member in the inherently closed path, which is traversed always in the same direction, makes separately acted upon engagement and disengagement means superfluous. The primary portion of the device, consisting of a double lever, a guide arm with detent member, and closed path, is simple in construction and thus is not susceptible to disturbances and is practically service-free. The double lever, arranged, for example, horizontally, and disposed along the rear side of the long base of the machine, makes it possible in a simple way to locate the point of engagement of the linkage connecting the double lever to the operating lever which is disposed on the front face. The operating lever is operable, for example, by an individual's knee or arm, in the zone of the machine base which is especially advantageous for this purpose, i.e., remote from the actual working zone of the sewing machine.